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Good point re CaCl2 used for deicing. As you probably know, in a former
life I made the Microcontaminometer. With the smallest tank, it could
measure down to picograms NaCl equivalent. I had some thoroughly cleaned
samples, 1" x 1" ceramic hybrid wafers, on my bench for testing.
Suddenly, they showed ionic contamination levels much higher than they
should have, which puzzled me. I was pondering on this when I saw a salt
(NaCl) sprinkler going along the road and light dawned. The tyres of
cars passing kicked up an aerosol of slush and salt that presumably
evaporated leaving a suspension of submicroscopic salt crystals that
floated everywhere including into my lab, which was a good 20 m from the
road (and the windows were shut!). This hypothesis was confirmed on a
number of subsequent occasions.
Similarly, I had a customer in Rennes at the foot of the Brittany
peninsula, about 50 km from the coast. He told me that his PCBs showed
consistently slightly higher ionic contamination readings when a violent
north-westerly Atlantic storm was raging.
However, tap water is the most probable source of Ca.
I'm afraid that 1 ppm is meaningless as such unless we know the area
from which the aliquot was derived. 1 ppm from a sample the size of an
A4 paper sheet would be bugger all in terms of reliability but it may be
a different story if the sample was a small passive component.
Brian
On 11.02.2014 00:08, Richard Kraszewski wrote:
> I am occasionally seeing irritating low levels of calcium in some assemblies that we test via ion chromatography.
>
> Some organizations required spec levels as low as <1 ppm.
>
> My questions to you techies is:
>
> #1 Besides wash water are there any other sources of calcium that come to mind?
>
> #2 is there any real value in having Calcium specs down as low as 1 ppm? (I suspect not and this spec was merely carried over from the semiconductor industry where it may have more value)
>
> CH65 is of some help here in that is does speak much more of the evils of Na that Ca& Mg, but not as much as I had hoped.
>
> Thoughts??
>
> Rich� Kraszewski
> Senior Process Engineer
> Plexus Engineering Solutions
>
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